Kinetic study of heavy metals Cu and Zn removal during sewage sludge ash calcination in air and N₂ atmospheres

Heavy metal control is essential during the thermochemical recovery of phosphorus (P) from sewage sludge ash (SSA). For medium volatile heavy metals, i.e. Cu and Zn, the effect of chlorine additive was complicated and more sensitive to temperature variation. So, in the in-depth study on the removal kinetics of Cu and Zn was necessary. Thus, the studies described in this paper considered the experiments and kinetic models of Cu and Zn removal in SSA through calcination under different atmospheres and temperatures. The results showed that within 15 min, the removal of Cu and Zn was more effective at the same temperature in air than in N₂. The result is consistent with kinetic analysis: Reaction activation energy of both Cu and Zn in an air atmosphere is lower than in N₂. In addition, the reaction orders, energy and frequency factors of Cu and Zn removal reaction during SSA calcination at high temperature with air and N₂ atmosphere were calculated.